Could it be simply static electricity? Perhaps this fellow was creating friction somehow, say between his clothing and the saddle. If subsequently he moved his body in a certain way that caused his skin to come into contact with the frame (steering through an obstacle or bracing for a bump, etc.), could he not sustain a shock? This possibility assumes that he must move in much the same manner every time he passes that spot.

Straws? I gots a handful. :confused:

-Rob